The present invention relates to a projector for displaying images, and more specifically pertains to a polarizer that is disposed on a light-incoming side and/or a light-outgoing side of a liquid crystal device.
Projectors have a liquid crystal light valve including a liquid crystal device (a liquid crystal panel). Polarizers are generally disposed on a light incoming surface and a light outgoing surface of the liquid crystal device. The polarizer functions to transmit a predetermined polarized light component, while removing the other light components.
A light absorbing-type polarizing plate is generally used for the polarizer in the projector. A typical example of the light absorbing-type polarizing plate is obtained by uniaxially orienting a film including iodine or dye molecules. The light absorbing-type polarizing plate has a relatively high extinction rate and relatively small incident angle dependency but poor light resistance and heat resistance.
The recent demand for the enhanced brightness of projected images and the size reduction of the projector leads to higher output of the light source device and size reduction of the liquid crystal device. This increases the luminous flux of light entering the polarizing plate and thereby raises the luminous flux density. Namely this raises the intensity of light entering the polarizing plate per unit area.
The raised intensity of light entering the polarizing plate per unit area undesirably increases thermal load applied to the polarizing plate. The light absorbing-type polarizing plate removes a non-required light component by absorption and converts the absorbed light component into heat. The light absorbing-type polarizing plate has poor light resistance and heat resistance and accordingly has difficulties in maintaining the polarization characteristics over a long time period. The disadvantage of the prior art projector is thus incapability of stably displaying high-contrast, bright images over a long time period.
The object of the present invention is thus to solve the drawbacks of the prior art technique discussed above and provide a projector that stably displays high-contrast, bright images by improving light resistance and heat resistance of a polarizer.
At least part of the above and the other related objects is attained by a projector as a first apparatus of the present invention. The projector includes: a light source device; an electro-optic device that modulates light emitted from the light source device; two polarizers that are disposed respectively on a light incoming side and a light outgoing side of the electro-optic device; and a projection optical system that projects light output from the electro-optic device. At least one of the two polarizers is a structural birefringent polarizing plate.
The structural birefringent polarizing plate may also be called a shape birefringent polarizing plate or a form birefringent polarizing plate.
This projector utilizes the structural birefringent polarizing plate, which hardly absorbs light and has relatively high light resistance and heat resistance. The projector thus stably displays high-contrast, bright images, even when the light entering the polarizer has a high intensity per unit area, due to an increase in light output of the light source device or due to reduction of the size of the electro-optic device.
When non-polarized light enters the polarizer disposed on the light incoming side of the electro-optic device, the thermal load applied to the polarizer on the light incoming side becomes heavier than the thermal load applied to the polarizer on the light outgoing side. In such cases, it is preferable that the structural birefringent polarizing plate is provided at least on the light incoming side of the electro-optic device.
When a predetermined polarized light enters the polarizer disposed on the light incoming side of the electro-optic device, the thermal load applied to the polarizer on the light outgoing side becomes heavier than the thermal load applied to the polarizer on the light incoming side. In such cases, it is preferable that the structural birefringent polarizing plate is provided at least on the light outgoing side of the electro-optic device.
In the above projector, the structural birefringent polarizing plate may be a wiregrid polarizing plate.
The wiregrid polarizing plate has a simple structure, which facilitates manufacture of the structural birefringent polarizing plate.
In accordance with one preferable application of the above projector, the structural birefringent polarizing plate includes a light transmissive crystal substrate and a fine periodic structure periodically formed in a predetermined direction on the light transmissive crystal substrate.
The light transmissive crystal substrate has a relatively high thermal conductivity and thus quickly releases heat generated by absorption of light by the structural birefringent polarizing plate. A sapphire substrate or a rock crystal substrate are typical examples of the light transmissive crystal substrate.
In accordance with another preferable application of the above projector, the structural birefringent polarizing plate is inclined to a center axis of light illuminating the electro-optic device.
The inclined layout of the structural birefringent polarizing plate practically decreases the pitch of the fine periodic structure relative to the incident light, thus improving the optical characteristics of the structural birefringent polarizing plate.
In the above application, the structural birefringent polarizing plate may be arranged at an inclination of about 45 degrees relative to the center axis.
When the light transmitted through the structural birefringent polarizing plate is utilized for the electro-optic device, this arrangement causes a non-required light reflected by the structural birefringent polarizing plate to be emitted in the direction of about 90 degrees to the center axis. This arrangement prevents adverse effects of the non-required light on other optical elements. This arrangement further enables the light reflected by the structural birefringent polarizing plate to be utilized for the electro-optic device.
In accordance with still another preferable application of the above projector, the structural birefringent polarizing plate is divided into a plurality of areas, and at least one of the plurality of areas is inclined to a center axis of light illuminating the electro-optic device.
This arrangement relatively decreases the thickness of the inclined structural birefringent polarizing plate (that is, the dimension in the direction perpendicular to the light incoming surface of the electro-optic device). Part of the plurality of areas may be arranged perpendicular to the center axis of the light illuminating the electro-optic device (that is, parallel to the light incoming surface of the electro-optic device).
In the above application, at least one of the plurality of areas in the structural birefringent polarizing plate may be arranged at an inclination of about 45 degrees relative to the center axis.
When the light transmitted through the structural birefringent polarizing plate is utilized for the electro-optic device, this arrangement causes the light reflected by the structural birefringent polarizing plate to be emitted in the direction of about 90 degrees to the center axis. This effectively prevents adverse effects of the reflected light on other optical elements. For the effective use of the light reflected by the structural birefringent polarizing plate, the reflected light may be returned to the light source device for recycling.
In accordance with one preferable embodiment of the above projector, a light absorbing polarizing plate is further arranged on a light outgoing side of the structural birefringent polarizing plate.
The optical characteristics of the structural birefringent polarizing plate have relatively large incident angle dependency and wavelength dependency. The optical characteristics of the light absorbing polarizing plate, on the other hand, have relatively small incident angle dependency and wavelength dependency. The combined use of the light absorbing polarizing plate compensates for the incident angle dependency and the wavelength dependency of the structural birefringent polarizing plate, thus attaining the polarizer having excellent light resistance, heat resistance, and optical characteristics. The structural birefringent polarizing plate and the light absorbing polarizing plate may be optically integrated with each other. The optical integration reduces the loss of light occurring at their interface. A polarizing plate composed of an iodine or dye-containing material may be applied for the light absorbing polarizing plate.
In the projector of the above application, it is preferable that a light transmissive crystal substrate is further arranged on a light outgoing side of the light absorbing polarizing plate, and the light transmissive crystal substrate is appressed to the light absorbing polarizing plate.
The arrangement of the light absorbing polarizing plate in close contact with the light transmissive crystal substrate having a relatively large thermal conductivity facilitates release of the heat generated by absorption of light by the light absorbing polarizing plate. This arrangement thus relieves the deterioration of the optical characteristics of the structural birefringent polarizing plate and the light absorbing polarizing plate, due to the heat generated by the light absorbing polarizing plate.
In accordance with another preferable embodiment of the above projector, a light reflective polarizing plate is further arranged on a light outgoing side of the structural birefringent polarizing plate.
The light reflective polarizing plate may be a multi-layered polarizing plate that is obtained by alternatively laminating a birefringent film and non-birefringent film.
The combined use of the light reflective polarizing plate, instead of the light absorbing polarizing plate, effectively compensates for the incident angle dependency and the wavelength dependency of the structural birefringent polarizing plate, thus attaining the polarizer having excellent light resistance, heat resistance, and optical characteristics.
The present invention is further directed as its second apparatus to a projector including: a light source device; an electro-optic device that modulates light emitted from the light source device; two polarizers that are disposed respectively on a light incoming side and a light outgoing side of the electro-optic device; and a projection optical system that projects light output from the electro-optic device. At least one of the two polarizers includes: a first prism having a light incoming surface and a light outgoing surface, which face to each other in a non-parallel orientation; and a light reflective polarizing plate that is disposed on a side of the light outgoing surface of the first prism. The light reflective polarizing plate divides light emitted from the first prism into first and second polarized lights having different polarizing directions, and transmits the first polarized light while reflecting the second polarized light. An angle defined by the light incoming surface and the light outgoing surface of the first prism is set to cause the second polarized light, which has been reflected by the light reflective polarizing plate and returned to the first prism, to be totally reflected by the light incoming surface.
This projector utilizes the light reflective polarizer including the light reflective polarizing plate. This polarizer hardly absorbs light and has relatively high light resistance and heat resistance. The projector thus stably displays high-contrast, bright images, even when the light entering the polarizer has a high intensity per unit area, due to an increase in light output of the light source device or due to reduction of the size of the electro-optic device.
This polarizer prevents the second polarized light reflected by the light reflective polarizing plate from being emitted from the light incoming surface of the prism to the outside. The light reflective polarizer disposed on the light outgoing side of the electro-optic device in the projector causes no light from the light reflective polarizer to enter the light outgoing surface of the electro-optic device, thus desirably preventing malfunction of the electro-optic device.
This polarizer has a prism. The relatively small setting for the angle defined by the light incoming surface and the light outgoing surface of the prism reduces the size of the polarizer and thereby the total size of the projector.
In accordance with one preferable application of the above projector, the first prism has an intersection line defined by the light incoming surface and the light outgoing surface, and the intersection line is substantially parallel to longer sides of a rectangular display area on the electro-optic device.
This arrangement further reduces the size of the polarizer and thereby the total size of the projector.
In accordance with another preferable application of the above projector, a face of the first prism opposite to a vertical angle defined by the light incoming surface and the light outgoing surface of the first prism is set to cause the second polarized light totally reflected by the light incoming surface to enter the opposite face at substantially right angles.
This arrangement causes the light entering the opposite face to be mostly emitted from the opposite face, thus significantly decreasing the light that is reflected by the opposite face and re-enters the light reflective polarizing plate.
In the above projector, it is preferable that the first prism is composed of a material having a photoelastic constant of not higher than about 1 nm/cm/105 Pa.
The prism composed of a material having a relatively low photoelastic constant causes substantially no change in polarizing state of the light passing through the prism. The polarizer accordingly exerts the excellent optical characteristics.
In one preferable application, the projector further includes a second prism, which is disposed on a light outgoing side of the light reflective polarizing plate to receive the first polarized light transmitted through the light reflective polarizing plate.
The traveling direction of the light emitted from the polarizer is regulated by adequately setting the refractive index of the second prism and the angle defined by the light incoming surface and the light outgoing surface of the second prism. This enhances the degree of freedom in layout of other optical parts. Setting the shape and the refractive index of the second prism to be identical with those of the first prism gives the polarizer with substantially no change in traveling direction of the transmitted light.
In the above application, it is preferable that at least one of the first prism and the second prism is composed of a material having a photoelastic constant of not higher than about 1 nm/cm/105 Pa.
In the above application, it is also preferable that the second prism is arranged to make a travelling direction of the first polarized light emitted via the second prism substantially coincide with a travelling direction of light entering the first prism.
This arrangement makes the traveling direction of the light entering the polarizer substantially coincident with the traveling direction of the light emitted from the polarizer, thus readily constructing the optical system including other optical parts. The coincidence of the traveling directions is attained by setting the refractive index of the second prism practically equal to the refractive index of the first prism, by arranging the light incoming surface of the second prism substantially parallel to the light outgoing surface of the first prism, and by arranging the light outgoing surface of the second prism substantially parallel to the light incoming surface of the first prism.
In accordance with one preferable embodiment of the above projector, a light absorbing polarizing plate is disposed on a light outgoing side of the light reflective polarizing plate.
The light absorbing polarizing plate compensates for the incident angle dependency and the wavelength dependency of the light reflective polarizing plate, thus giving the polarizer having excellent light resistance, heat resistance, and optical characteristics. When the polarizer includes the second prism, the light absorbing polarizing plate may be disposed either on the light incoming side or on the light outgoing side of the second prism.
In the above projector, the light reflective polarizing plate may be a structural birefringent polarizing plate.
The structural birefringent polarizing plate is a light reflective polarizing plate that hardly absorbs light and has relatively high light resistance and heat resistance. The light reflective polarizer stably exerts the high optical characteristics even when the light entering the polarizer has a high intensity per unit area. A typical example of the structural birefringent polarizing plate is a wiregrid polarizing plate.
In one preferable example of the above arrangement, the structural birefringent polarizing plate has a fine periodic structure periodically formed along a predetermined direction, and the predetermined direction is substantially perpendicular to an intersection line defined by the light incoming surface and the light outgoing surface of the first prism.
This causes the structural birefringent polarizing plate to be inclined to the center axis of the light illuminating the electro-optic device. Such inclination practically decreases the pitch of the fine periodic structure relative to the incident light, thus improving the optical characteristics of the structural birefringent polarizing plate.
In the above projector, the light reflective polarizing plate may be a multi-layered polarizing plate that is obtained by alternatively laminating a birefringent film and non-birefringent film.
Application of the multi-layered polarizing plate for the light reflective polarizing plate relatively reduces the incident angle dependency and the wavelength dependency.
The present invention is also directed its third apparatus to a projector including: a light source device; an electro-optic device that modulates light emitted from the light source device; two polarizers that are disposed respectively on a light incoming side and a light outgoing side of the electro-optic device; and a projection optical system that projects light output from the electro-optic device. At least one of the two polarizers includes a plurality of polarizer elements. Each polarizer element has: a first prism having a light incoming surface and a light outgoing surface, which face to each other in a non-parallel orientation; and a light reflective polarizing plate that is disposed on a side of the light outgoing surface of the first prism. The plurality of polarizer elements are jointed in such a manner that the respective light incoming surfaces of the first prisms are located in a virtually same plane. In each polarizer element, the light reflective polarizing plate divides light emitted from the first prism into first and second polarized lights having different polarizing directions, and transmits the first polarized light while reflecting the second polarized light. An angle defined by the light incoming surface and the light outgoing surface of the first prism is set to cause the second polarized light, which has been reflected by the light reflective polarizing plate and returned to the first prism, to be totally reflected by the light incoming surface.
The polarizer included in the second apparatus discussed above is used for the polarizer elements, so that this projector exerts the same functions and advantages as those of the projector of the second apparatus. Compared with the second apparatus using an integral polarizer, this arrangement decreases the thickness of each polarizer element and thereby reduces the total size of the polarizer. Application of the polarizer having the above construction to the projector advantageously reduces the whole size of the projector, compared with the projector of the second apparatus.
The present invention is also directed as its fourth apparatus to a polarizer including: a first prism having a light incoming surface and a light outgoing surface, which face to each other in a non-parallel orientation; and a light reflective polarizing plate that is disposed on a side of the light outgoing surface of the first prism. The light reflective polarizing plate divides light emitted from the first prism into first and second polarized lights having different polarizing directions, and transmits the first polarized light while reflecting the second polarized light. An angle defined by the light incoming surface and the light outgoing surface of the first prism is set to cause the second polarized light, which has been reflected by the light reflective polarizing plate and returned to the first prism, to be totally reflected by the light incoming surface.
This polarizer is same with the polarizer used in the second apparatus of the present invention and accordingly exerts the same functions and advantages.
The present invention is further directed as its fifth apparatus to a polarizer that includes a plurality of polarizer elements. Each polarizer element has: a first prism having a light incoming surface and a light outgoing surface, which face to each other in a non-parallel orientation; and a light reflective polarizing plate that is disposed on a side of the light outgoing surface of the first prism. The plurality of polarizer elements are jointed in such a manner that the respective light incoming surfaces of the first prisms are located in a virtually same plane. In each polarizer element, the light reflective polarizing plate divides light emitted from the first prism into first and second polarized lights having different polarizing directions, and transmits the first polarized light while reflecting the second polarized light. An angle defined by the light incoming surface and the light outgoing surface of the first prism is set to cause the second polarized light, which has been reflected by the light reflective polarizing plate and returned to the first prism, to be totally reflected by the light incoming surface.
This polarizer is same with the polarizer used in the third apparatus of the present invention and accordingly exerts the same functions and advantages.